Overhead and underground telephone lead-in cable for voice, data and video transmission services

ABSTRACT

An improved overhead or underground telephone lead-in cable for transmission services VVDL (voice, video, data and lead-in) that permits the connection of the users to the public telephone system with a high speed digital service link, besides the analog services required. The cable has at least one or a plurality of transmission circuits. One of the transmission circuit is formed by two metal conductor elements cooperating in turn to self-support the cable or a conventional type of impregnated fibers or kevlar tape. The second circuit which is formed by a stranded pair of conductors is impregnated with a swelling powder preventing moisture penetration.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The instant invention relates to an overhead or underground telephonelead-in cable for VVDL-type services (voice, video, data and lead-in)permitting the connection of the users to the public telephone systemwith high speed digital services link besides offering analog services.This is made possible through the integration of a balanced circuit tothe original design of two elements made of metal, plastic of kevlarfibers, in parallel, also serving as self-supporting elements inoverhead installation. Said cable is characterized because its core isprotected by a moisture resistant film and is thus highly convenient foroverhead or underground installation.

2. Previous Art

Generally, the overhead lead-in lines of the unitary telephone serviceshave been limited with regard to their bandwidth and resistance to radiointerferences because of their design. The demand for transmission meansable to support a bandwidth large enough to meet the growing demand fordigital services in the coming years also requires designs that do notincrease the costs or limit the ease of installation of the currentproducts. With regard to the cables used for the connection of the usersto the telephone network, the design is a decisive factor. The cableshould be light and economical and permit high-speed data transmissionabove 155 Mbps. It should also have an adequate response in frequenciesabove 100 Mhz and be self-supporting over distances spanning more than100 meters. Moreover, the cable should be weather-resistant and in windyand icy conditions, it should permit its reinforcement without beingnecessary to modify its shape, so that the same anchorage elementsusually used in this type of services can be utilized.

Among the known techniques used to solve the above-mentioned problems,in U.S. Pat. No. 4,467,138 a “conductive cable for pluralcommunications” is described, the design of which is related to a flatcommunication conductor. Said flat communication conductor has two omore communication ports, polyolefin insulated cables united throughoutits length arranged in groups on opposed and parallel sides of aconductive steel wire.

Even though cables presenting stranded pairs of conductors are known,not all of them have the same application, i.e. depending on their use,the design varies in each case and even the number of pitches of thestranded pair presents differences. For example, in U.S. Pat. No.6,064,008 a communication cable having two pair of stranded conductorsis described, the main characteristic of which it is not the strandedpairs but the insulating filling material based on a chemical product offluorinated polymer with a blowing agent. In U.S. Pat. No. 6,509,526 D,anteriority of the instant invention, a telephone lead-in cable isdescribed for ordinary voice service and high performance Data and Videotransmission services. Said cable is based on a thermoplastic sleeve,with a data transmission circuit having two metal wires helically unitedwithin a thin protective band resisting to temperatures up to 240° C. Atthe center of said thermoplastic sleeve a circuit element for voicetransmission based on two parallel metal conductors is arranged. Eachone of said metal conductors is opposed to the helical union of thefirst circuit.

Thus, for example in U.S. Pat. No. 4,761,053 an overhead lead-in cableis described which includes a rectangular cross-section sleeve with twotension members based on various filaments impregnated with a sleevecompatible material. Each said member is arranged opposite a pair ofconductors and at least one of them is made of optic fiber andvertically aligned, in parallel.

In U.S. Pat. No. 5,180,890 a cable is described which is also of arectangular type, including two tension members, one placed at each endof the sleeve and two copper conductors separated and horizontallyaligned, in parallel.

In U.S. Pat. No. 5,155,304 an overhead lead-in cable is described withan embodiment of 4 or more tension members based on intertwinedfilaments impregnated with a plastic material forming a reinforcementthread for the catenary elongation tension. Said overhead lead-in cablealso has two or more insulated copper conductors placed in the center ofthe thermoplastic sleeve, vertically aligned and in parallel or in theshape of a cross forming and interstice between the insulatedconductors.

The applicant has developed an improved VVDL-type lead-in cable foroverhead or underground installation, based on a design ofself-supporting elements for overhead lead-in lines and a dedicatedcircuit permitting a high-speed digital signal transmission withoutinterfering at all with the voice service signals or the use ofadditional electronic circuits to separate the signals. The design thatis also highly resistant to diaphony, is characterized because it has acore of two insulated conductors impregnated with a surrounding layer ofmoisture absorbing swelling powder.

DESCRIPTION OF THE INVENTION

The accompanying drawings, which are incorporated in and constitute partof this specification, are included to illustrate and provide a furtherunderstanding of the instant invention.

FIG. 1 is an isometric view with a cross-section of the telephonelead-in cable for data and voice transmission services (VVDL), showingthe distribution of its elements with moisture protection layer.

FIG. 2 is a cross-sectional view of FIG. 1, showing the arrangement ofone or more transmission circuits in a cable and only with the moistureprotection.

FIG. 3 is a cross-sectional view of FIG. 1, showing the helical reunionof the fusion protection tape and with a swelling material layer.

The main object of the new Voice, Video and Data (VVDL) telephonelead-in cable is to prevent moisture penetration into the core of theVVDL cable, when it is used in overhead service and exposed to moisturepenetration from rain, or when said cable is installed in undergroundducts and directly exposed to extremely moist environments. The coreformed by two insulated conductors is characterized because itincorporates outside around the conductors a moisture absorbing powderfilm of swelling material preventing water penetration inside said core.

The film is applied alternately through an electrostatic system when theexternal cover of the cable is applied. Said system permits thedistribution of the film in a controlled way, and the deposit of theswelling material in a quantity that is proportional to the requiredthickness of said film. The VVDL-type (Voice, Video, Data, Lead-in)lead-in cable (A) includes two self-supporting metal elements foroverhead lead-in lines 10, 11 and can also transmit voice signals whenthe members are made of metal because, between them, they create anadditional circuit dedicated to the transmission of analog signals. Italso includes a circuit permitting the transmission of data at relativehigh speed formed by two metal wires 12 and 13 individually insulatedwith a polyolefinic material, polyethylene or polypropylene, andstranded together, forming a balanced circuit of 100 ohms impedance 15,FIG. 1, 2 and 3. It is characterized by a high resistance to diaphonythat could occur through the conjugation of the elements in the sametransmission plane. The stranded pair of insulated wires 15 or balancedcircuit can be covered by a very thin mylar tape 16 of a materialresisting at temperatures up to 240° C., only when said thermalprotection is required by the installation conditions. Between theconductive elements of the circuits 12 and 13 and the protective film 16or sleeve 18 area when it is not included into said film 16, a swellingpowder layer based on a superabsorbing polymer is formed. The protectivelayer 17 is against direct moisture when the cable is installedunderground or against rain the cable is for overhead installation. Thecircuit and self-supporting members are extruded with a thermoplasticmaterial 18 protecting them against the environment and facilitating thehandling of the cable in installation in spans longer than 100 meters.The geometrical figure of the cable (A) permits said cable to besubmitted to tension or compression through anchorage elements withoutany of the transmission components being damaged which could deteriorateits electrical characteristics.

Lead-in Cable (VVDL) FIGS. 1 to 3

The cable object of the instant invention (A), is a rectangularelongated body at the ends of which corner pieces are placed 19, whichare rounded for better installation handling. Said cable also presentsrecesses 20 in its lateral ends, in the middle part, to create asemi-rectangular geometrical shape submitted to lower tensile stress.

The lead-in cable (A) has, equidistantly distributed in its structure18, one or several transmission circuits, which do not require for theirinstallation any special type of fittings for fixing them onto theterminal distribution post or box of the telephone network and the houseof the consumer or user of the telephone services. The voice circuitelements are preferably placed in the stranded pair of wires 12 and 13of the central core 15, but can also been incorporated in the tensionmembers 10, 11 when they are made of metal conductors acting asself-supporting elements. In this case, said elements 10, 11 are made ofmetal cylindrical conductors, without limitation as to their compositionand cross section, i.e., the elements can be of metal alloys orcomposition of two metals tempered with a treatment permitting a highrupture strength. This is because said elements are self-supporting andare also supporting the other elements conforming the cable. However,the thermal treatment must be between 45° C. and 550° C. Through atreatment of this type, said conductors or self-supporting metalelements do not substantially lose their resistance characteristics tothe passage of electrical current. Said elements 10, 12 are placedlongitudinally in parallel between them and are separated by a 4 to 6 mmdistance permitting the placement of the second transmission circuit 15between them. Said elements are arranged to offer an appropriated meansfor transmitting digital signals 12 at relatively high speeds (155Mbps). They are made of quasi cylinder mild copper metal conductors,100% pure and stranded with a smooth surface of a diameter of 0.5 to0.64 mm, permitting spans on distances of up to 150 meters and withrelatively low losses of 22 Db/100 at 100 MHz. Each one of theconductive elements is individually insulated with a thermoplasticcompound layer 14 applied continuously and highly uniform insuring aconcentricity of the wall of insulating material with regard to theconductor above 90%. Said insulating layer can be applied in only onelayer or in various layers and each one of the insulating layers iscolored to facilitate its identification. The material used for layerscan be solid, expanded through physical or chemical action or can havecompounds delaying or inhibiting flame propagation. The insulatedconductors are stranded 15, forming a pair or balanced circuit thedistance between each strand of the conductors being such that itpermits to minimize the diaphony effects caused by the proximity ofother element emitting electromagnetic signals and to reduce the exit ofenergy towards the other circuit. The stranded pair 15 shows an optimumperformance because the control of the wall thickness and the helix ofeach one of the stranded conductors to form the pair insure thestability of the characteristic impedance at relative high frequencies.Moreover, the circuit remains in an excellent electrical balanceminimizing in this way the interference of external agents. The balancecircuit or stranded pair 15 is optionally covered by a thin tapeprotecting against melting, made of temperature resistant material, 16applied helicoidally or longitudinally onto said protective cover whenit is required for the installation. The tape prevents a melting of theinsulation material among themselves and/or among the compound of thecover during the application of the outer cover 18 through an extrusionprocess, and because of heat transfer from the compound to the insulatedconductors. Moreover, this tape also acts as a barrier to prevent theinvasion of the transmission area of the balanced circuit by thecompound of the cover. It also acts as a barrier to prevent themodification of its dielectric constant and in turn its characteristicimpedance that increases the circuit loss because of a highercapacitance. It also presents a cover reinforced by its design based ona thermoplastic compound 18 forming an integral body and maintaining theself-supporting elements on each side and diametrically parallelopposite to the stranded pair.

The space between the protection tape 16 and the core of the strand 15,is impregnated through electrostatic means with a layer of swellingpowder material which is a poly(sodium acrylate) homopolymer commercialproduct.

The cover 18 protects both elements against mechanical damage that couldbe caused during the storage, transportation and installation. Thecompound of the cover is weather resistant according to the installationarea and protects also the circuits against premature aging through theaction of sun, water or any other external agent. This compound can alsobe flame retardant if it is required where the cable is installed.

The design of the cable body has a rectangular geometrical shape withtrimmed edges 19, and recesses 20 permitting the product to be installedusing any of the fixing fittings currently designed. Moreover, it ispossible to avoid that the components be damaged by the tensile andcompression stresses to which they are submitted during installation anddaily functioning.

ADVANTAGES OF THE INVENTION

The advantage of the cable design is the tensile strength, i.e. theincrease of the installation span distance that can be solved throughthe change of the cross section of the support elements or the type ofmaterial used in their manufacturing.

The use of swelling powder on the paired core permits the direct use ofthe cable in underground installations because the absorbing materialprevents the penetration of the moisture usually found in undergroundinstallation areas.

VVDL Cable Characteristics

Additionally, the cable withstands a crushing test of 1000 lb/f (14.88kg/cm) which meets the underground conditions. The cable of U.S. Pat.No. 6,509,526 B2 includes 24 AWG conductors as components of theconductive core of the VVDL cable while the instant invention permitsthe development of new cable constructions from 16 to 26 AWG cables.

The electrical performance of the new VVDL cable of two 24 AWGconductors fulfils the following electrical characteristics. TABLE 1Electrical Characteristics Characteristics Unit Specified ResistanceOhms/km 89.5 max. Resistance Unbalance % 5 max. Insulation resistanceMegaohms/km 5000 min. Mutual capacitance NF/km 75 max. Groundingcapacitance unbalance PF/km 2595 max. High voltage between conductorsVDC 1200

TABLE 2 Frequency MHz Attenuation dB/100 m 1 2.20 4 4.62 8 6.88 10 7.8516 10.46 20 12.03 25 13.88 31.25 16.04 62.5 25.62 100 35.78

TABLE 3 Mechanical and dimensional characteristics of the cableCharacteristics Unit Specified Gauge AWG 24 Conductor diameter mm  0.51rated Insulation diameter mm 0.904 rated Width (A) mm 5.50 ± 0.35 Height(B) mm 4.10 ± 0.35 Channel Width (D) mm 15 Depth © mm 0.27 Rupture loadKgf 80 Packing length m 250 Approx. weight Kg/km 32The self-supporting members, i.e. the tensile members 10, 11 are made ofconventional glass fibers impregnated with polymers or kevlar tapes whenthe lead-in cable includes only one transmission circuit.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the lead-in cable of theinstant invention without departing from the spirit or scope of saidinvention. Thus, the present invention is not limited by the foregoingdescriptions but is intended to cover all modifications and variationsthat come within the scope of the spirit of the invention and the claimsthat follow.

1-32. (canceled)
 33. An overhead or underground telephone lead-in cablefor voice, video and data (VVDL) transmission services, comprising: arectangular structure comprising a rectangular outer cover having ageometrical shape comprising a thermoplastic material; at least one or aplurality of transmission circuit comprising: a self-supporting membercomprising two conducting elements; said elements arranged at theopposite ends, in parallel, and in turn are diametrically opposed to thetransmission circuit; said cable comprising a core having a pair ofstranded conductors placed at the center of the rectangular structure ofthe cable wherein said conductors are insulated by a thermoplasticcompound layer; a swelling layer surrounding said core which isdeposited electrostatically as a moisture protection element; and anextruded cover reinforced with a thermoplastic material forming thelead-in cable.
 34. The overhead or underground telephone lead-in cablefor transmission services (VVDL) of claim 33 wherein the conductingelements are made of a material selected from the group consisting ofmetal, alloys, fiber glass and combination thereof.
 35. The overhead orunderground telephone lead-in cable for transmission services (VVDL) ofclaim 33 wherein the conducting elements are impregnated with a materialselected from a group consisting of polymers, kevlar tapes and mylartapes.
 36. The overhead or underground telephone lead-in cable fortransmission services (VVDL) of claim 35 wherein the polymers areselected from a group consisting of polyolefins, polyethylene,polypropylene and combinations thereof.
 37. The overhead or undergroundtelephone lead-in cable for transmission services (VVDL) of claim 33,wherein the circuit formed by a stranded pair of balanced circuitpresents a characteristic impedance of 100 ohms.
 38. The overhead orunderground telephone lead-in cable for transmission services (VVDL) ofclaim 33, wherein the swelling layer comprises a swelling powder whichis a conventional poly(sodium acrylate) homopolymer compound.
 39. Theoverhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 33, wherein the swelling layer iselectrostatically applied to form a cover layer on the stranded pairduring the extrusion of a flame resistant reinforced thermoplasticcover.
 40. The overhead or underground telephone lead-in cable fortransmission services (VVDL) of claim 33 wherein the self supportingmember is made of metal.
 41. The overhead or underground telephonelead-in cable for transmission services (VVDL) of claim 40 wherein theself supporting member acts as additional circuit with regard to thecore, enhancing the transmission of voice signals such that theyconstitute a circuit oriented to the transmission of analog signals. 42.The overhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 33, wherein the circuit of the stranded pairpermits the transmission of digital signal data at speeds of 155 Mbps.43. The overhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 33, wherein the pair of conductors are strandedwith a smooth surface at a diameter of 0.5 to 0.64 mm.
 44. The overheador underground telephone lead-in cable for transmission services (VVDL)of claim 33, wherein the cable permits to span distances of up to 150meters, and the distance between each strand of the conductors permitsto reduce the diaphony effects caused by the nearness of other elementemitting electromagnetic signals, as well as reduce the loss of energyto the other circuit.
 45. The overhead or underground telephone lead-incable for transmission services (VVDL) of claim 33, wherein in each oneof the conductors, the core is insulated with a thermoplastic layer. 46.The overhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 45, wherein the insulation is appliedcontinuously and uniformly such that the concentricity of the wall ofinsulating material with regard to the conductor is higher than 90% andcan be colored for identification purposes.
 47. The overhead orunderground telephone lead-in cable for transmission services (VVDL)according to claim 33 further comprising a thin thermoplastic sleeve asa protecting element against melting heat of up to 240° C.
 48. Theoverhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 47, wherein the swelling layer furthercomprises a filler, which serves as a moisture protective element and isdeposited electrostatically and arranged between the area around thethin sleeve and the core of the stranded conductors.
 49. The overhead orunderground telephone lead-in cable for transmission services (VVDL) ofclaim 33 wherein the conductors of the core or self-supporting member ofthe metal cables are elements selected from the group consisting ofcopper, alloys and combination thereof.
 50. The overhead or undergroundtelephone lead-in cable for transmission services (VVDL) of claim 33wherein the conductors are subjected to thermal treatments.
 51. Theoverhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 33 wherein the thermal treatment is between 45°C. and 550° C.
 52. The overhead or underground telephone lead-in cablefor transmission services (VVDL) of claim 33 wherein the stranded pairfurther comprises optionally a covering of a thin protecting tapematerial comprising a temperature resistant material and appliedhelicoidally or longitudinally onto the protective element.
 53. Theoverhead or underground telephone lead-in cable for transmissionservices (VVDL) of claim 33 wherein the space between the thinprotecting tape material and the stranded conductor is impregnatedthrough electrostatic means with the swelling layer.
 54. The overhead orunderground telephone lead-in cable for transmission services (VVDL) ofclaim 33 which permits development of cable constructions from at least16 AWG to 26 AWG conductors as components of the core.
 55. The overheador underground telephone lead-in cable for transmission services (VVDL)of claim 33 further comprising trimmed edges and recesses to permitinstallation of the product.
 56. The overhead or underground telephonelead-in cable for transmission services (VVDL) of claim 33 comprising: arectangular structure comprising a rectangular outer cover having ageometrical shape comprising a thermoplastic material; at least one or aplurality of transmission circuit comprising: a self-supporting membercomprising two conducting elements; said elements arranged at theopposite ends, in parallel, and in turn are diametrically opposed to thetransmission circuit; said cable comprising a core having a pair ofstranded metal conductors placed at the center of the rectangularstructure of the cable wherein said conductors are insulated by athermoplastic compound layer; a thin thermoplastic sleeve as protectingelement against melting heat of up to 240° C.; a filler of swellinglayer surrounding said core which is deposited electrostatically betweenthe area around the thin sleeve and the core of stranded conductors as amoisture protection element; and an extruded cover reinforced with athermoplastic material forming the lead-in cable.